From: Michal Hocko <mhocko@kernel.org>
To: Hugh Dickins <hughd@google.com>
Cc: Baoquan He <bhe@redhat.com>, David Hildenbrand <david@redhat.com>,
linux-mm@kvack.org, pifang@redhat.com,
linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
aarcange@redhat.com, Mel Gorman <mgorman@suse.de>,
Vlastimil Babka <vbabka@suse.cz>
Subject: Re: Memory hotplug softlock issue
Date: Mon, 19 Nov 2018 21:59:07 +0100 [thread overview]
Message-ID: <20181119205907.GW22247@dhcp22.suse.cz> (raw)
In-Reply-To: <alpine.LSU.2.11.1811191215290.15640@eggly.anvils>
On Mon 19-11-18 12:34:09, Hugh Dickins wrote:
> On Mon, 19 Nov 2018, Michal Hocko wrote:
> > On Mon 19-11-18 15:10:16, Michal Hocko wrote:
> > [...]
> > > In other words. Why cannot we do the following?
> >
> > Baoquan, this is certainly not the right fix but I would be really
> > curious whether it makes the problem go away.
> >
> > > diff --git a/mm/migrate.c b/mm/migrate.c
> > > index f7e4bfdc13b7..7ccab29bcf9a 100644
> > > --- a/mm/migrate.c
> > > +++ b/mm/migrate.c
> > > @@ -324,19 +324,9 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
> > > goto out;
> > >
> > > page = migration_entry_to_page(entry);
> > > -
> > > - /*
> > > - * Once page cache replacement of page migration started, page_count
> > > - * *must* be zero. And, we don't want to call wait_on_page_locked()
> > > - * against a page without get_page().
> > > - * So, we use get_page_unless_zero(), here. Even failed, page fault
> > > - * will occur again.
> > > - */
> > > - if (!get_page_unless_zero(page))
> > > - goto out;
> > > pte_unmap_unlock(ptep, ptl);
> > > - wait_on_page_locked(page);
> > > - put_page(page);
> > > + page_lock(page);
> > > + page_unlock(page);
> > > return;
> > > out:
> > > pte_unmap_unlock(ptep, ptl);
>
> Thanks for Cc'ing me. I did mention precisely this issue two or three
> times at LSF/MM this year, and claimed then that I would post the fix.
I've had a recollection about some issue I just couldn't remember what
was it exactly. Tried to make Vlastimil to remember but failed there as
well ;)
> I'm glad that I delayed, what I had then (migration_waitqueue instead
> of using page_waitqueue) was not wrong, but what I've been using the
> last couple of months is rather better (and can be put to use to solve
> similar problems in collapsing pages on huge tmpfs. but we don't need
> to get into that at this time): put_and_wait_on_page_locked().
>
> What I have not yet done is verify it on latest kernel, and research
> the interested Cc list (Linus and Tim Chen come immediately to mind),
> and write the commit comment. I have some testing to do on the latest
> kernel today, so I'll throw put_and_wait_on_page_locked() in too,
> and post tomorrow I hope.
Cool, it seems that Baoquan has a reliable test case to trigger the
pathological case.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-11-19 20:59 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-14 7:09 Memory hotplug softlock issue Baoquan He
2018-11-14 7:16 ` Baoquan He
2018-11-14 8:18 ` David Hildenbrand
2018-11-14 9:00 ` Baoquan He
2018-11-14 9:25 ` David Hildenbrand
2018-11-14 9:41 ` Michal Hocko
2018-11-14 9:48 ` David Hildenbrand
2018-11-14 10:04 ` Michal Hocko
2018-11-14 9:01 ` Michal Hocko
2018-11-14 9:22 ` David Hildenbrand
2018-11-14 9:37 ` Michal Hocko
2018-11-14 9:39 ` David Hildenbrand
2018-11-14 14:52 ` Baoquan He
2018-11-14 15:00 ` Michal Hocko
2018-11-15 5:10 ` Baoquan He
2018-11-15 7:30 ` Michal Hocko
2018-11-15 7:53 ` Baoquan He
2018-11-15 8:30 ` Michal Hocko
2018-11-15 9:42 ` David Hildenbrand
2018-11-15 9:52 ` Baoquan He
2018-11-15 9:53 ` David Hildenbrand
2018-11-15 13:12 ` Baoquan He
2018-11-15 13:19 ` Michal Hocko
2018-11-15 13:23 ` Baoquan He
2018-11-15 14:25 ` Michal Hocko
2018-11-15 13:38 ` Baoquan He
2018-11-15 14:32 ` Michal Hocko
2018-11-15 14:34 ` Baoquan He
2018-11-16 1:24 ` Baoquan He
2018-11-16 9:14 ` Michal Hocko
2018-11-17 4:22 ` Baoquan He
2018-11-19 10:52 ` Baoquan He
2018-11-19 12:40 ` Michal Hocko
2018-11-19 12:51 ` Michal Hocko
2018-11-19 14:10 ` Michal Hocko
2018-11-19 16:36 ` Vlastimil Babka
2018-11-19 16:46 ` Michal Hocko
2018-11-19 16:46 ` Vlastimil Babka
2018-11-19 16:48 ` Vlastimil Babka
2018-11-19 17:01 ` Michal Hocko
2018-11-19 17:33 ` Michal Hocko
2018-11-19 20:34 ` Hugh Dickins
2018-11-19 20:59 ` Michal Hocko [this message]
2018-11-20 1:56 ` Baoquan He
2018-11-20 5:44 ` Hugh Dickins
2018-11-20 13:38 ` Vlastimil Babka
2018-11-20 13:58 ` Baoquan He
2018-11-20 14:05 ` Michal Hocko
2018-11-20 14:12 ` Baoquan He
2018-11-21 1:21 ` Hugh Dickins
2018-11-21 1:08 ` Hugh Dickins
2018-11-21 3:20 ` Hugh Dickins
2018-11-21 17:31 ` Michal Hocko
2018-11-22 1:53 ` Hugh Dickins
2018-11-14 10:00 ` Michal Hocko
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